1. Field of the Invention
The present invention relates to a fuel supply apparatus for an internal combustion engine having a high pressure fuel pipe for supplying fuel, which has been pressurized by a high pressure fuel pump, to an injector of the internal combustion engine, and a seal member arranged in a fuel transfer portion of the high pressure fuel pipe for securing a sealing property.
2. Description of the Related Art
A cylinder fuel injection type internal combustion engine is structured to pressurize a fuel in a fuel tank to a high pressure by a supply pump, supply the pressurized fuel to a high pressure fuel pipe formed of a delivery pipe and the like, and directly inject and supply the fuel into a cylinder from the injector connected to the delivery pipe.
Further, fuel pressure within the high pressure fuel pipe, that is, an injection pressure of the fuel injected from the injector is controlled to a pressure suitable for an operating state of the internal combustion engine. For example, the injection pressure is controlled by controlling a discharge amount of the supply pump. In this case, the fuel pressure in the high pressure fuel pipe is normally set to be higher than that of an inlet port of fuel injection type internal combustion engine. This is because the fuel has to be injected against an internal pressure of the highly pressurized cylinder in case of the cylinder fuel injection type internal combustion engine. Further, the fuel spray is required to be atomized to secure a good combustion state.
In the fuel supply apparatus employed in the cylinder fuel injection type internal combustion engine, a seal member like O-ring has been conventionally place at a location where fuel leakage is likely to occur. For example, the O-ring has been placed at a connection portion between the delivery pipe and the injector, a connection portion between the supply pump and the delivery pipe or the like such that sufficient sealing property is obtained. The aforementioned technique is disclosed in Japanese Patent Application Laid-Open No. HEI 9-126087 or Japanese Patent Application Laid-Open No. HEI 10-73060. The technique for securing the sealing property for the connection portion using the seal member is not a complicated operation. Additionally, the O-ring is effective at damping vibrations transmitted to the high pressure fuel pipe from the supply pump.
However, the aforementioned seal member is likely to loose its flexibility and lose sealing ability when exposed to a low temperature. Accordingly, in the fuel supply apparatus using a seal member there has been a risk of leakage of a very small amount of fuel from the connection portion of the high pressure fuel pipe where the seal member is attached. For example, a leak may occur when cold starting the internal combustion engine.